In the medical field, it is frequently desirable to take biopsy samples from a patient. Two major fields of biopsy procedures exist. One field is known as "soft-tissue biopsy" and the other field is known as "bone marrow biopsy". In the bone marrow biopsy field, it is always necessary to puncture the bone of a patient in order to retrieve bone marrow which normally exists only in the center of a bone.
It may be desirable to retrieve bone marrow for several different reasons. In one type of bone marrow procedure, it is desirable to retrieve a "core" of bone marrow to examine bone marrow architecture. This procedure may be useful in determining whether a patient has cancer and the extent of cancerous cells that may exist. Examining a bone marrow core typically involves an extended period of time in which the core is first prepared and then sliced into thin samples which are examined under a microscope.
In other bone marrow procedures, it is desirable to simply aspirate a portion of the bone marrow to make a relatively rapid determination of the number of bone particles in the sample to indicate the state of a patient's disease. Aspirated bone marrow can be further studied to aid in the diagnosis of a patient.
Finally, in other bone marrow procedures, multiple aspirations of bone marrow are conducted to perform a bone marrow transplant. While each of these procedures have different goals, they all require that the bone be punctured in order to access the bone marrow within. Thus, it is important to provide a needle which enhances the ability of the user to puncture bone with minimal trauma to the patient.
All bone marrow biopsy, aspiration and transplant needles currently on the market have a handle with a cannula extending outwardly from the handle. The handle is used by the doctor to apply force to the cannula as the cannula punctures the bone. Such needles typically include a stylet with a sharpened tip which is inserted through the cannula and is used to initially puncture the bone. The stylet is then removed and bone marrow is withdrawn from the patient by manipulating the cannula to cause bone marrow to move into the interior of the cannula. In some cases a slight suction is applied to the cannula to hold the bone marrow in place as the cannula is removed from the patient.
Bone marrow needles have traditionally been designed so that the needle is attached to the center of the handle. While many physicians feel comfortable with a centrally attached needle, it has been recently discovered that it may be easier to guide a needle with a users' index finger if the needle is not centrally located on the handle of the needle assembly. It has also recently been discovered that when an off-center device is used, it is important to insure that a physician's arm, wrist, and index finger are all generally in alignment with the cannula of the needle to provide enhanced control over the needle. These discoveries are discussed in greater detail below with regard to the present invention.
Also, bone marrow needle tips have traditionally been formed using a single angular grind which essentially produces a single cutting surface. Such a needle tip is described in U.S. Pat. No. 4,469,109. Refinements have been made to the needle tip over the years. For example, U.S. Pat. No. 4,838,282 describes a stylet and cannula in which the stylet extends beyond the length of a cannula and in which the stylet and cannula have angular surfaces which are parallel to one anther and, thus, mate with one another. While at least one other manufacturer has developed a cannula with more than one cutting surface, the cannula is intended to be used with a stylet that has cutting surfaces that are in direct alignment with the cutting surfaces of the cannula. The present invention seeks to improve upon the cutting features of both the stylet and of the cannula without requiring that the cutting surfaces of the cannula mate with the cutting surfaces of the stylet.
Another feature of most bone marrow needle assemblies currently on the market is that when the stylet is removed from the cannula, the shape of the handle typically is materially changed. For example, the bone marrow needle assembly described in U.S. Pat. No. 4,838,282 involves removing approximately half of the handle assembly when the stylet is removed from the cannula. It has recently been discovered, as part of the subject invention, that it is desirable to maintain the original shape of the handle as much as possible after the stylet has been removed to allow a physician to more easily manipulate the cannula within a patient's bone.